1. Field of the Invention
This invention relates to processes associated with drying loose materials, and more particularly to apparatus for conductive drying loose materials.
2. Description of the Prior Art
There is known an apparatus (cf., USSR Inventor's Certificate No. 918,752, Int. Cl. F 26 B 17/26, published 1982) for drying loose materials including metal chips containing combustibles. The apparatus comprises a drying chamber over which there is disposed a furnace separated from the drying chamber by a perforated partition wall, a heat exchanger for heating balls of a headpiece, a magnetic drum for separating the headpiece balls from chip when the headpiece is heated to the Curie point (for iron-carbon alloys the Curie point is +768.degree. C.), an oscillating conveyer of the drying chamber, and an elevator for returning the balls of the headpiece for reuse.
The material is heated and dried in the drying chamber upon contact with the heated balls.
Oil evaporating from the material is subjected to reburning, the oil vapour entering through the perforated partition from the drying chamber to the furnace thereby providing extra heat utilized for heating the headpiece balls in the heat exchanger.
One disadvantage of this prior art apparatus is that it cannot be used oro drying fusible alloys having a melting point below the Curie point, heating to this point being necessary for separating the balls of the headpiece from the magnetic drum.
The provision of the elevator for returning the balls of the headpiece, the magnetic drum, and oscillating conveyer in the drying chamber requires consumption of an excessive amount of energy for the drying process.
The apparatus is not capable of high thermal efficiency, since for removing moisture and oil it is necessary to heat the material to a temperature of 200.degree. C. to 350.degree. C., whereas the headpiece must be heated to 768.degree. C. to be separated from the magnetic drum.
Waste gases escaping from the apparatus have the same high temperature thus making the consumption of heat energy substantial. In addition, in the course of conveying, the balls of the headpiece tend to lose heat transferring it to the elevator and oscillating conveyer.
There also is known a drum-type undirect heating apparatus for drying loose materials (cf., West German Pat. No. 2,060,027, Cl. 82a 19/01, published 1973). The apparatus comprises a housing accommodating inner and outer tubes arranged concentrically relative to each other. Flue or waste gas is withdrawn through the inner tube in a direction counter to the travel path of the material in the drying chamber confined between the walls of the inner and outer tubes, rigidly interconnected and capable of being rotated by an external drive. The interior of the heating chamber is defined by a space between the walls of the housing and outer tube. Connected to the housing is a furnace communicating with the heating chamber. A flare of the outer tube of the drying chamber extends to a discharge means and is connected to a device for suctioning the vapours of moisture and oil. The drying chamber is isolated from the heating chamber by sealing members. The heating chamber communicates with the interior of the inner tube through a flue chamber in turn communicable with the discharge means. The inner tube of the drying chamber is connected with a worm, which is in contact with the walls of the outer tube connected to a second worm.
Inherent in this prior art apparatus is a disadvantage in that oil evaporated from the material being dried is not utilized by secondary burning, and therefore the potential heat from such oil vapours is not used as an additional source of energy, which makes this apparatus less energy efficient.
Another disadvantage resides in that the heating process is carried out without evacuation of the evaporated oil and moisture to result in oxidation and carbonization of the material.
In addition, the horizontal arrangement of the drum of the drying chamber determines the large size of the apparatus.